Commit 559c758b authored by David Kaplan's avatar David Kaplan Committed by Borislav Petkov (AMD)
Browse files

x86/bugs: Restructure MDS mitigation 



Restructure MDS mitigation selection to use select/update/apply
functions to create consistent vulnerability handling.

  [ bp: rename and beef up comment over VERW mitigation selected var for
    maximum clarity. ]

Signed-off-by: default avatarDavid Kaplan <david.kaplan@amd.com>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: default avatarJosh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/20250418161721.1855190-2-david.kaplan@amd.com
parent d9b79111

arch/x86/kernel/cpu/bugs.c

+59 −2
Original line number Diff line number Diff line
@@ -34,6 +34,25 @@ 


#include "cpu.h"



/*

 * Speculation Vulnerability Handling

 *

 * Each vulnerability is handled with the following functions:

 *   <vuln>_select_mitigation() -- Selects a mitigation to use.  This should

 *				   take into account all relevant command line

 *				   options.

 *   <vuln>_update_mitigation() -- This is called after all vulnerabilities have

 *				   selected a mitigation, in case the selection

 *				   may want to change based on other choices

 *				   made.  This function is optional.

 *   <vuln>_apply_mitigation() -- Enable the selected mitigation.

 *

 * The compile-time mitigation in all cases should be AUTO.  An explicit

 * command-line option can override AUTO.  If no such option is

 * provided, <vuln>_select_mitigation() will override AUTO to the best

 * mitigation option.

 */



static void __init spectre_v1_select_mitigation(void);

static void __init spectre_v2_select_mitigation(void);

static void __init retbleed_select_mitigation(void);
@@ -41,6 +60,8 @@ static void __init spectre_v2_user_select_mitigation(void); 
static void __init ssb_select_mitigation(void);

static void __init l1tf_select_mitigation(void);

static void __init mds_select_mitigation(void);

static void __init mds_update_mitigation(void);

static void __init mds_apply_mitigation(void);

static void __init md_clear_update_mitigation(void);

static void __init md_clear_select_mitigation(void);

static void __init taa_select_mitigation(void);
@@ -172,6 +193,7 @@ void __init cpu_select_mitigations(void) 
	spectre_v2_user_select_mitigation();

	ssb_select_mitigation();

	l1tf_select_mitigation();

	mds_select_mitigation();

	md_clear_select_mitigation();

	srbds_select_mitigation();

	l1d_flush_select_mitigation();
@@ -182,6 +204,14 @@ void __init cpu_select_mitigations(void) 
	 */

	srso_select_mitigation();

	gds_select_mitigation();



	/*

	 * After mitigations are selected, some may need to update their

	 * choices.

	 */

	mds_update_mitigation();



	mds_apply_mitigation();

}



/*
@@ -284,6 +314,12 @@ enum rfds_mitigations { 
static enum rfds_mitigations rfds_mitigation __ro_after_init =

	IS_ENABLED(CONFIG_MITIGATION_RFDS) ? RFDS_MITIGATION_AUTO : RFDS_MITIGATION_OFF;



/*

 * Set if any of MDS/TAA/MMIO/RFDS are going to enable VERW clearing

 * through X86_FEATURE_CLEAR_CPU_BUF on kernel and guest entry.

 */

static bool verw_clear_cpu_buf_mitigation_selected __ro_after_init;



static void __init mds_select_mitigation(void)

{

	if (!boot_cpu_has_bug(X86_BUG_MDS) || cpu_mitigations_off()) {
@@ -294,12 +330,34 @@ static void __init mds_select_mitigation(void) 
	if (mds_mitigation == MDS_MITIGATION_AUTO)

		mds_mitigation = MDS_MITIGATION_FULL;



	if (mds_mitigation == MDS_MITIGATION_OFF)

		return;



	verw_clear_cpu_buf_mitigation_selected = true;

}



static void __init mds_update_mitigation(void)

{

	if (!boot_cpu_has_bug(X86_BUG_MDS) || cpu_mitigations_off())

		return;



	/* If TAA, MMIO, or RFDS are being mitigated, MDS gets mitigated too. */

	if (verw_clear_cpu_buf_mitigation_selected)

		mds_mitigation = MDS_MITIGATION_FULL;



	if (mds_mitigation == MDS_MITIGATION_FULL) {

		if (!boot_cpu_has(X86_FEATURE_MD_CLEAR))

			mds_mitigation = MDS_MITIGATION_VMWERV;

	}



		setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);

	pr_info("%s\n", mds_strings[mds_mitigation]);

}



static void __init mds_apply_mitigation(void)

{

	if (mds_mitigation == MDS_MITIGATION_FULL ||

	    mds_mitigation == MDS_MITIGATION_VMWERV) {

		setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);

		if (!boot_cpu_has(X86_BUG_MSBDS_ONLY) &&

		    (mds_nosmt || cpu_mitigations_auto_nosmt()))

			cpu_smt_disable(false);
@@ -602,7 +660,6 @@ static void __init md_clear_update_mitigation(void) 


static void __init md_clear_select_mitigation(void)

{

	mds_select_mitigation();

	taa_select_mitigation();

	mmio_select_mitigation();

	rfds_select_mitigation();